Abstract We present results from Atacama Large Millimeter/submillimeter Array (ALMA) observations of CS from the nearby galaxy NGC 1068 (∼14 Mpc). This Seyfert 2 barred galaxy possesses a circumnuclear disc (CND, r ∼ 200 pc) and a starburst ring (SB ring, r ∼ 1.3 kpc). These high-resolution maps (∼0.5″, ∼35 pc) allow us to analyse specific sub-regions in the galaxy and investigate differences in line intensity ratios and physical conditions, particularly those between the CND and SB ring. Local thermodynamic equilibrium (LTE) analysis of the gas is used to calculate CS densities in each sub-region, followed by non-LTE analysis conducted using the radiative transfer code RADEX to fit observations and constrain gas temperature, CS column density and hydrogen density. Finally, the chemical code UCLCHEM is used to reconstruct the gas, allowing an insight into its origin and chemical history. The density of hydrogen in the CND is found to be ≥105 cm−2, although exact values vary, reaching 106 cm−2 at the AGN. The conditions in the two arms of the SB ring appear similar to one another, though the density found (∼104 cm−2) is lower than in the CND. The temperature in the CND increases from east to west, and is also overall greater than found in the SB ring. These modelling methods indicate the requirement for multi-phase gas components in order to fit the observed emission over the galaxy. A larger number of high resolution transitions across the SLED may allow for further constraining of the conditions, particularly in the SB ring.

A giant undulation event observed at SANAE, Antarctica (L = 4) is reported. During the event the geomagnetic activity was high, as was the case in previously reported observations of giant undulations. Data were recorded by all‐sky and small field‐of‐view TV cameras, from 2346 UT on September 10, to 0007 UT on September 11 (MLT ∼ 2200 h) 1987. The fine temporal and spatial resolution of the TV data made a detailed study of the undulation possible. The average wavelength was 170 km and the amplitude of the wave increased from 70 km to 140 km in 10 minutes. Wave propagation, measured at different positions on the undulation, was duskward with a phase speed of 540 to 650 m/s. An inner structure, propagating at a speed of 2.5 to 4.0 km/s, about 3 times as fast as the undulation form, was observed just poleward of the undulation boundary, indicating the presence of strong velocity shear. The linear theory of the velocity shear instability is examined as a possible generation mechanism on the basis of these observations.

Simultaneous measurements of ionospheric electric fields by STARE and TV imaging of pulsating auroral forms strongly suggest that the latter undergo E×B drift. A display of pulsating auroras is considered as the projection on the ionosphere of an assembly of ducts of enhanced plasma density convecting with the background plasma. Energetic electrons, convecting and with additional gradient and curvature drift, sweep through these ducts which are ‘illuminated’ by pulsating precipitation of these energetic electrons. Both the self‐sustained pulsation model of Davidson (1979) and the driven pulsation model of Coroniti and Kennel (1970) are compatible with our observations.

Stanford and Ziemke [1993] have recently demonstrated the versatility of the Total Ozone Mapping Spectrometer (TOMS) data set in characterizing the behaviour of Rossby‐gravity waves. Similar analyses performed here are extended to relate interannual differences in Southern Hemisphere mid‐latitude wave activity to the severity of the Antarctic ozone depletion. Total ozone wave powers for wavenumber 1 to 6 have been calculated from TOMS distributions for each day from 1979 to 1992 and a mean measure of Antarctic ozone depletion has been determined for each year. After normalization with respect to stratospheric chlorine loading, interannual differences in the severity of the Antarctic ozone hole are anti‐correlated with total wave powers. Furthermore, wintertime mean wave power and polar stratospheric temperatures are well correlated and appear to lag the equatorial Quasi‐biennial Oscillation (QBO) by 1 year.

Abstract. In an earlier paper [Kosch et al., 1998], simultaneous all-sky TV imager and Scandinavian Twin Auroral Radar Experiment (STARE) observations of an ionospheric plasma vortex located poleward of an auroral arc were presented. The vortex is associated with a sudden brightening of the arc and corresponds to an ionospheric region of diverging horizontal electric fields, which is equivalent to a downward field-aligned current (FAC), i.e., the closure current for the upward current above the arc. This event has been revisited because of the subsequent availability of data from the Scandinavian Magnetometer Array. These data, combined with STARE electric fields, have been used to determine the real ionospheric conductance distribution throughout the field of view. As a result, a more realistic, quantitative picture of the current system associated with the arc is obtained than was possible in an earlier model based on an assumed constant conductance. In particular, a complete macroscopic electrodynamic description of a plasma vortex, composed of ionospheric conductances, true horizontal currents, and FACs, is obtained for the first time. It is shown that the plasma vortex corresponds to an area of decreased conductance, thus broadening the FAC distribution and reducing the current density compared to the earlier results. The study illustrates that horizontal conductance gradients should not be neglected when computing FACs. IntroductionThe precipitation of energetic particles in, for example, auroral arcs can result in small-scale longitudinal and latitudinal conductivity gradients. Such conductivity gradients, which can also be highly variable in time, occur within localized regions of as little as 1-20 km, the width of auroral arcs. Strong conductivity gradients modify the convection-driven electrojets and [1993] have proposed the following scenario based on satellite measurements. A current system associated with auroral arcs consists of a matched pair of magnetic fieldaligned currents (FACs). The upward current flowing above the arc and the downward return current flowing on the poleward (equatorward) side of the arc in the postmidnight (premidnight) sector are connected by a Pedersen current in the ionosphere. Since the Pedersen current will flow in the direction of the convection electric field (equatorward postmidnight and poleward premidnight), this determines on which side of the optical arc the radar arc is observed. The upward current is carried by the energetic precipitating electrons responsible for the auroral arc. The downward current is carried by upward fluxes of low-energy ionospheric electrons outside of the arc, resulting in a depletion of ionospheric conductivity in that region. If the magnetospheric process resulting in an auroral arc acts as a current generator, then the ionospheric electric field has to modify itself in such a way that current continuity in the ionosphere is preserved. Therefore the meridional electric field has to increase, in conjunction with an enhanced ionospheric...